Analysis And Improvement Of Quantum State Deterministic Remote Preparation And Quantum Steganography Protocols In Noisy Environment

Quantum communication utilizes the characteristics of quantum entanglement and non-cloning principle to realize secure communication.Compared with classical communication,quantum communication has the characteristics of easy preparation and theoretical unconditional security and it will play a vital role in the future communication field.However,in the actual communication process,the quantum system in communication is inevitably coupled with environment,resulting in serious deviations between the actual communication and the ideal result.Therefore,it is an urgent problem to discuss the influence of noise and improve the performance of communication protocols in actual communication process.This thesis analyzes two important types of quantum communication technologies(deterministic quantum state remote preparation and quantum steganography protocols)in order to find out the influence rules and optimization methods of quantum noise.The contents discussed and studied in this thesis are as follows:(1)The effects of four main noises(amplitude damping,phase damping,bit flip,and depolarizing noise)in quantum channels on deterministic remote quantum state preparation protocols are studied and corresponding optimization method.First,in order to explore the relationship between the influence of noise,the entangled resources used in the remote preparation scheme,as well as the particle allocation and measurement methods,three different deterministic remote preparation schemes(based on ?-state,Brown state and GHZ state,and the particle allocation and measurement methods are different)are selected and the output states and fidelities of the three preparation schemes under four noise environments are calculated.The calculation results show that under the same kind of noise,the output states and fidelities of the three preparation schemes are the same.The influence of quantum noise is only related to the type of noise,noise intensity and the target quantum state.The effects of noise when preparing specific two-qubit states were further explored.The results show that in this case,bit flip has no effect on the protocols,while depolarizing noise has the greatest effect.Finally,possible strategies to reduce the impact of quantum noise are discussed.Secondly,we turn to the influence of quantum noise on the deterministic remote preparation protocol for the preparation of arbitrary three-qubit states,and explore whether the preparation of three-qubit states has the same conclusion as the preparation of two-qubit states.Taking two protocols for the preparation of arbitrary three-qubit states(based on ? state and Brown state and using different auxiliary particles,respectively)as examples,the effects of quantum noise on the two preparation protocols are discussed.The results show that under the same noise environment,quantum states prepared by the two preparation protocols are the same and the final quantum states are only related to quantum states to be prepared and noise intensity coefficients.In addition,under the premise of known noise intensity,if the prepared quantum state coefficient can be adjusted,the influence of quantum noise can be reduced by adjusting the quantum state coefficient.(2)The effects of four kinds of quantum noise(amplitude damping,phase damping,bit flip,and depolarizing)on the quantum steganography protocol are investigated and corresponding improvement scheme which can improve the fidelity of transmitting information is proposed by utilizing the nature of noise.Taking the large payload steganographic protocol based on Bell state as an example,the possible situation of quantum noise and its impact on the steganographic protocol are studied.The fidelity of the transmitted ordinary information carried by a single qubit after being affected by different noises is calculated,and then the fidelity of secret information under the influence of noise is calculated.The results show that when different noises are superimposed during transmission,the fidelity of the transmitted information may be increased and the specific measures are discussed when dealing with different noises.In order to further discuss the application of noise superposition to resist quantum noise in quantum steganography,the influence of noise on ?-state steganography protocol was calculated in detail.The results show that when the noise intensity is strong,in addition to amplitude damping noise,the effect of noise can be reduced by superimposing additional noise.Specifically,phase damping and bit flip noise can be suppressed by superimposing phase flip noise,and depolarizing noise can be suppressed by superimposing depolarizing noise.